Steering angle sensing apparatus and method thereof

ABSTRACT

A steering angle sensing apparatus and method are provided. The apparatus and method sense the steering angle of a steering shaft by using a rotated bit value difference corresponding to the rotated angles of magnets, which are respectively coupled on an axis of one of a plurality of sub gears, when the sub gears with respectively different gear ratios rotate with a shaft gear that rotates together with the steering shaft.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.11/997,553, filed Jan. 31, 2008, now U.S. Pat. No. 7,841,231, issuedNov. 30, 2010, which is the U.S. national stage application ofInternational Patent Application No. PCT/KR2007/003414, filed Jul. 13,2007, which claims priority to Korean Patent Application Nos.10-2006-0069564, filed Jul. 25, 2006, 10-2006-0101333, filed Oct. 18,2006, 10-2006-0101871, filed Oct. 19, 2006, and 10 -2007-0067496, filedJul. 5, 2007, all of which are incorporated herein by reference in theirentirety.

TECHNICAL FIELD

Embodiments relate to a steering angle sensing apparatus and a steeringangle sensing method.

BACKGROUND ART

A steering mechanism that is an indispensable part of an automobile is amechanism that alters the path and direction of travel of the automobileaccording to a driver's wishes. Such a steering mechanism includes asteering wheel controlled by the a driver, a steering shaft connected tothe steering wheel for relaying the steering inputs from the driver, anda sensing apparatus installed on the steering shaft for sensing theangle of the steering wheel (steering angle).

Typically, a steering wheel connected to a steering shaft is capable ofrotating 2-3 turns clockwise and counterclockwise. A steering sensorcapable of accurately detecting the rotated direction and steering angleof a steering shaft is required.

TECHNICAL PROBLEM

Embodiments provide a steering angle sensing apparatus and methodcapable of detecting an absolute steering angle by digitally processingthe rotated angles of magnets coupled to the shafts of a plurality ofsub gears rotated by a shaft gear.

Embodiments provide a steering angle sensing apparatus and methodcapable of reducing the margin for errors caused by signal changes,through digital processing following rotated angle sensing of aplurality of magnets.

TECHNICAL SOLUTION

An embodiment provides a steering angle sensing apparatus comprising: ashaft gear coupled to a steering shaft; a first sub gear rotating withthe shaft gear; a second sub gear engaged with the first sub gear, andhaving a gear ratio different from a gear ratio of the first sub gear; afirst magnet coupled on an axis of the first sub gear; and a secondmagnet coupled on an axis of the second sub gear.

An embodiment provides a steering angle sensing apparatus comprising: afirst magnet rotating with a gear coupled to a steering shaft gear; asecond magnet rotating at a rotation cycle different from the firstmagnet; a first angle detecting portion outputting a first rotated bitvalue corresponding to a change in a magnetic field of the rotatingfirst magnet; a second angle detecting portion outputting a secondrotated bit value corresponding to a change in a magnetic field of therotating second magnet; and a steering angle calculating portioncalculating a steering angle using a difference between the firstrotated bit value of the first angle detecting portion and the secondrotated bit value of the second angle detecting portion.

An embodiment provides a steering angle sensing method comprising:rotating a shaft gear coupled to a steering shaft; rotating a pluralityof sub gears with mutually different gear ratios together with the shaftgear; outputting respective rotated bit values corresponding to changesin magnetic fields of a plurality of magnets, the magnets respectivelycoupled on an axis of each of the sub gears; and obtaining a steeringangle of the steering shaft through using a difference in rotated bitvalues of the plurality of magnets.

ADVANTAGEOUS EFFECTS

An advantage of the above-structured steering angle sensing apparatusand method according to the embodiment is that an absolute steeringangle can be detected using a simple calculation by digitally outputtingrotated angles of magnets that rotate at respectively different ratesaccording to the rotation of a shaft gear.

Also, the possibilities of errors occurring during signal conversion canbe reduced by eliminating the process of converting analog signals todigital signals.

Additionally, because there is no process of converting signals,reliability and processing speed are improved, and a cost reduction canbe derived from the omission of an analog/digital converter.

Furthermore, a smaller steering angle sensing apparatus can be provided.

Moreover, a combined sensor that senses steering angle as well assteering angle torque can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a steering angle sensing apparatusaccording to a first embodiment.

FIG. 2 is a perspective view of a steering angle sensing apparatusaccording to a second embodiment.

FIG. 3 is a perspective view of a steering angle sensing apparatusaccording to a third embodiment.

FIG. 4 is a perspective view of a steering angle sensing apparatusaccording to a fourth embodiment.

FIG. 5 is a perspective view of a steering angle sensing apparatusaccording to a fifth embodiment.

FIG. 6 is block diagram of the steering angle sensor in FIG. 1 and asteering angle calculating unit.

FIG. 7 is a graph showing an example of deriving steering angles usingvalues outputted by an angle detecting portion based on the rotation oftwo shaft gears, according to steering angle sensing embodiments.

FIG. 8 is a flowchart of a steering angle sensing method according to afirst embodiment.

FIG. 9 is a flowchart of a steering angle sensing method according to asecond embodiment.

BEST MODE

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. Wherever possible, the same reference numbers will be usedthroughout the drawings to refer to the same or like parts.

FIG. 1 is a perspective view of a steering angle sensing apparatusaccording to a first embodiment.

Referring to FIG. 1, a steering angle sensing apparatus 200 includes ashaft gear 220 coupled to a steering shaft 100, a first sub gear 230, afirst magnet 231, a second sub gear 240, a second magnet 241, a firstangle detecting portion 251, a second angle detecting portion 252, and asteering angle calculating portion 255.

The steering angle sensing apparatus 200 may be provided within a case201 and a cover 202. The shaft gear 220, the first sub gear 230, thefirst magnet 231, the second sub gear 240, and the second magnet 241 aredisposed on the inner side of the case 201. A circuit board 250 isdisposed on the inner side of the cover 202, and the first angledetecting portion 251, the second angle detecting portion 252, and thesteering angle calculating portion 255 are disposed on the circuitboard. Here, the steering angle calculating portion 255 may be disposedon another circuit board.

When a driver manipulates a steering wheel (not shown) the movement istransferred through the steering shaft 100 to the shaft gear 220. Theshaft gear 220 is coupled to the outer circumference of the steeringshaft 100 and rotates together with the steering shaft 100. Here, theshaft gear 220 may be directly coupled to the steering shaft 100 orcoupled through the output shaft 210 of a steering torque sensor 203,and is not limited to these two conditions.

The steering torque sensor includes a torque sensor (not shown), atorsion bar (not shown), and the output shaft 210 installed within thecase 201.

The shaft gear 220 is coupled to the outer perimeter of the output shaft210 of the steering torque sensor 203. For example, a protrusion 223formed in the inner circumference of the shaft gear 220 inserts in aslot 213 formed in the outer circumference of the output shaft 210.Here, the positions and numbers of the protrusion 223 and the slot 213may be altered.

The shaft gear 220 rotates with the steering shaft 100 2-3 turns in aclockwise or counterclockwise direction. For example, the steering shaft100 may be designed to turn 720°-1080° in one direction, but is notlimited to this range of rotation.

The first sub gear 230 and the second sub gear 240 are respectivelyengaged to the shaft gear 220, and rotate together with the shaft gear220. The first sub gear 230 and the second sub gear 240 have differentgear ratios, and the gear ratio of the second sub gear 240 may begreater than the gear ratio of the first sub gear 230. For example, whenthe shaft gear 220 turns one revolution, the first sub gear 230 mayrotate more than the second sub gear 240.

As an example, if the shaft gear 220, the first sub gear 230, and thesecond sub gear 240 have a respective gear ratio of 1:8:7.5, when theshaft gear 220 rotates once, the first sub gear 230 rotates 8 times, andthe second sub gear rotates 7.5 times. The two sub gears are not limitedthereto, and the second sub gear may have a greater gear ratio than thefirst sub gear.

The first magnet 231 is coupled to the axis of the first sub gear 230,and rotates together with the first sub gear 230. The second magnet 241is coupled to the axis of the second sub gear 240, and rotates togetherwith the second sub gear 240. The first magnet 231 and the second magnet241 may be formed of one of a bipolar permanent magnet, electromagnet,and magnetized metal with at least two poles—N and S.

The first magnet 231 and the second magnet 241 rotate according to therotation of the first sub gear 230 and the second sub gear 240, andtheir magnetic fields change according to their rotation.

The first angle detecting portion 251 faces the first magnet 231 at auniform distance, and the second angle detecting portion 252 faces thesecond magnet at a uniform distance. Here, the spaces between the twoangle detecting portions 251 and 252 and the two magnets 231 and 241 maybe the same or different.

The first angle detecting portion 251 and the second angle detectingportion 252 are mounted on the circuit board 250 and may be formedrespectively of rotary hall integrated circuits (ICs). The rotary hallICs include at least a magnetic sensor. Such rotary hall IC sensorsdetect changes in magnetic fields according to the rotation of therespective magnets 231 and 241 in real time, and convert the detectedmagnetic field values into digital values for outputting.

The first angle detecting portion 251 and the second angle detectingportion 252 respectively detect the changes in the magnetic fields ofthe first and second magnets 231 and 241 according to the rotation ofthe shaft gear 220, and output digital data corresponding to thedetected changes in magnetic fields.

The steering angle calculating portion 255 first calculates thedifference between the digital data of the first angle detecting portion251 and the digital data of the second angle detecting portion 252, andthen detects an absolute steering angle corresponding to the differencein digital data values. Here, the absolute steering angle can accuratelydetect the steering portion of an automobile's steering wheels even whenelectrical power is turned off and back on. For this purpose, thecircuit board 250 may further include a storage portion (not shown) forstoring rotated bit values of the first angle detecting portion 251 andthe second angle detecting portion 252 and steering angles.

The operation of the above steering angle sensing apparatus 200 can bedescribed as follows.

When a driver handles a steering wheel, the steering shaft 100 connectedto the steering wheel turns. When the steering shaft 100 rotates, theshaft gear 220 rotates with the shaft.

The first sub gear 230 and the second sub gear 240 with respectivelydifferent gear ratios are rotated at different speeds by the shaft gear220.

Here, the first magnet 231 coupled on the axis of the first sub gear 230and the second magnet 241 coupled on the axis of the second sub gear 240rotate so that their magnetic fields are altered. For example, thepositions of the respective N and S poles of the first and secondmagnets 231 and 241 change according to the rotation of the first andsecond sub gears 230 and 240.

The first angle detecting portion 251 detects the rotated angle throughthe change in the magnetic field of the first magnet 231, and a firstrotated bit value corresponding to the rotated angle is outputted to thesteering angle calculating portion 255.

The second angle detecting portion 252 detects the rotated angle throughthe change in the magnetic field through the rotation of the secondmagnet 241, and a second rotated bit value corresponding to the rotatedangle is outputted to the steering angle calculating portion 255.

After the steering angle calculating portion 255 calculated the offsetbetween the first rotated bit value of the first angle detecting portion251 and the second rotated bit value of the second angle detectingportion 252, the steering angle of the steering shaft 100 is detectedusing the difference between the calculated rotated bit values. Thedetecting of the steering angle will be described in detail withreference to FIGS. 6 and 7.

FIG. 2 is a perspective view of a steering angle sensing apparatusaccording to a second embodiment. Like elements in the second and firstembodiments are given like reference numerals, and repetitivedescription thereof will not be given.

Referring to FIG. 2, a steering angle sensing apparatus 200 includes afirst sub gear 330 engaged to a shaft gear 220, and a second sub gear340 engaged to the first sub gear 330. The first sub gear 330 and thesecond sub gear 340 have respectively different gear ratios, and thegear ratio of the second sub gear 340 may be greater than the gear ratioof the first sub gear 330.

A first magnet 331 is coupled on the axis of the first sub gear 330, anda second magnet 341 is coupled on the axis of the second sub gear 340.Here, because the second sub gear 340 is meshed with the first sub gear330, the space between the first and second magnets 331 and 341 isreduced. Accordingly, the space between the first angle detectingportion 251 and the second angle detecting portion 252 facing the firstand second magnets 331 and 341 is reduced. Thus, the size of the circuitboard 250 can be reduced and the steering angle sensing apparatus 200can also be made smaller.

The first and second angle detecting portions 251 and 252 sense magneticfield changes when the first and second magnets 331 and 341 rotate, andrespectively output digital data on the magnetic field changes. Thesteering angle calculating portion 255 uses the difference in the outputdata of the first and second angle detecting portions 251 and 252 todetect the steering angle.

FIG. 3 is a perspective view of a steering angle sensing apparatusaccording to a third embodiment. Like elements in the third and firstembodiments are assigned like reference numerals, and repetitivedescriptions will not be given.

Referring to FIG. 3, the steering angle sensing apparatus 200 has afirst sub gear 430 engaged with a shaft gear 220, and a second sub gear440 engaged with connecting gear 432 formed on one side of the first subgear 430.

The connecting gear 432 has a lower gear ratio than the first sub gear430 and the second sub gear 440.

A first magnet 431 is coupled on the axis of the first sub gear 430 andthe connecting gear 432, and a second magnet 441 is coupled on the axisof the second sub gear 440. Here, the space between the first and secondmagnets 431 and 441 is less than in the first embodiment, so that thespace between the first angle detecting portion 251 and the second angledetecting portion 252 is reduced. Therefore, the size of the circuitboard 250 may be reduced, and the steering angle sensing apparatus 200may be made smaller.

The first and second angle detecting portions 251 and 252 detectmagnetic field changes according to the rotation of the first and secondmagnets 431 and 441, and output digital data on the magnetic fieldchanges. The steering angle calculating portion 255 uses the differencebetween the output data of the first and second angle detecting portions251 and 252 to detect the steering angle.

FIG. 4 is a perspective view of a steering angle sensing apparatusaccording to a fourth embodiment. Like elements in the fourth and firstembodiments are assigned like reference numerals, and repetitivedescriptions will not be given.

Referring to FIG. 4, in the steering angle sensing apparatus 200, aconnecting gear 520 is engaged with a shaft gear 220, and a first andsecond sub gear 530 and 540 are engaged to the connecting gear 520.

Here, a magnet is not provided on the axis of the connecting gear 520,and a first and second magnet 531 and 541 are coupled to the axes of thefirst and second sub gears 530 and 540. In the fourth embodiment, thefirst and second sub gears 530 and 540 are not directly meshed with theshaft gear 220, but are engaged indirectly through the connecting gear520.

Also, the first sub gear 530 has a gear ratio smaller than that of thesecond sub gear 540. The connecting gear 520 rotates according to therotating of the shaft gear 220, upon which the first and second subgears 530 and 540 also rotate.

Here, the first and second angle detecting portions 251 and 252 detectchanges in magnetic fields when the first and second magnets 531 and 541rotate, and respectively output digital data on the magnetic fieldchanges. The steering angle calculating portion 255 uses the differencebetween the output data of the first and second angle detecting portions251 and 252 to detect the steering angle.

FIG. 5 is a perspective view of a steering angle sensing apparatusaccording to a fifth embodiment. Like elements in the fifth and firstembodiments are assigned like reference numerals, and repetitivedescriptions will not be given.

Referring to FIG. 5, in the steering angle sensing apparatus 200, afirst sub gear 630 is engaged to the outer perimeter of the shaft gear220, and a second sub gear 640 is engaged to the inner circumference ofthe first sub gear 630. Thus, the gear ratio of the first sub gear 630is greater than the gear ratio of the second sub gear 640.

A first and a second magnet 631 and 641 are respectively coupled on theaxes of the first sub gear 630 and the second sub gear 640. Here, thesizes of the second sub gear 640 and the first magnet 631 may be made sothat the first magnet 631 does not cover the second sub gear 640.

Also, the distance between the first magnet 631 and the first angledetecting portion 251 may be different from the distance between thesecond magnet 641 and the second angle detecting portion 252.

Here, the first and second angle detecting portions 251 and 252 detectchanges in magnetic fields according to the rotation of the first andsecond magnets 631 and 641, and respectively output digital data on themagnetic fields. The steering angle calculating portion 255 uses thedifference in the digital data outputted by the first and second angledetecting portions 251 and 252 to detect the steering angle.

FIG. 6 is block diagram of the steering angle sensor in FIG. 1 and asteering angle calculating unit.

Referring to FIG. 6, the first angle detecting portion 251 detects afirst rotated angle according to a magnetic field shift with therotation of the first magnet 231, and outputs a first rotated bit value(S1) as digital data corresponding to the rotated angle.

The second angle detecting portion 252 detects a second rotated anglethrough a magnetic field shift according to the rotation of the secondmagnet 241, and outputs a second rotated bit value (S2) as digital datacorresponding to the second rotated angle.

The steering angle calculating portion 255 subtracts the second rotatedbit value S2 from the first rotated bit value S1 to obtain the rotatedbit offset, and multiplies rotated bit offset with a predetermined gainvalue to detect the steering angle of the steering wheel and steeringshaft. Here, the rotated bit value, the rotated bit offset, the gainvalue, and the steering angle are stored in a storage portion (notshown), and provided to the steering angle calculating portion 255.

This steering angle can be derived through Equation 1 below.θ=δS×G,  Equation 1

where θ is the steering angle, δS=S1−S2, and 0≦δS≦2^(n)−1, and G is thegain value.

S1 is the first rotated bit value corresponding to the rotated angle ofthe first magnet 231 detected by the first angle detecting portion 251,and S2 is the second rotated bit value corresponding to the rotatedangle of the second magnet 241 detected by the second angle detectingportion 252.

Here, δS is a value of the difference of the first rotated bit value S1and the second rotated bit value S2, where the maximum value is 2^(n)−1,and the minimum value is 0. The ‘n’ is the number of digital outputtedbits of the angle detecting portion.

The gain value G is a value that is preset according to differencesbetween the gear ratios of the shaft gear, the first sub gear, and thesecond sub gear and the rotated bits.

In this embodiment, the shaft gear is coupled to the steering shaft, andthe rotation of the shaft gear prompts the plurality of sub gears andthe plurality of magnets to rotate at different intervals. Also, theplurality of angle detecting portions 251 and 252 outputs digital dataaccording to changes in the magnetic fields for the plurality of magnets231 and 241, and the steering angle calculating portion 255 uses thedifference in the digital data to detect the absolute steering angle ofthe steering shaft. Thus, the steering angle calculating portion candirectly use the outputted digital data to quickly detect the steeringangle, so that reliability is improved and processing time is shortened.

FIG. 7 is a graph showing an example of deriving steering angles usingvalues outputted by an angle detecting portion based on the rotation oftwo shaft gears, according to steering angle sensing embodiments.

The x-axis in FIG. 7 represents the steering angle, and the maximumlock-to-lock steering angle (where the steering wheel is turned from anutmost clockwise position to an utmost counterclockwise position) may beset at 1800°. The y-axis represents the output values of the angledetecting portions and the steering angle calculating portion.

Referring to FIGS. 6 and 7, to obtain the first rotated bit value S1,after the rotated angle of the first magnet 231 detected by the firstangle detecting portion 251 is linearly obtained according to rotatingcycles, the rotated angle of each rotating cycle becomes the firstrotated bit value S1.

To obtain the second rotated bit value S2, after the rotated angle ofthe second magnet 232 detected by the second angle detecting portion 252is linearly obtained according to rotating cycles, the rotated angle ofeach rotating cycle becomes the second rotated bit value S2.

Here, the intervals are different due to the differences in gear ratios.That is, there is a difference between the rotating cycles of the firstmagnet 231 and the second magnet 232, and this difference can beobtained from the difference between the first rotated bit value S1 andthe second rotated bit value S2.

The rotated bit values S1 and S2 of the first and second magnets 231 and232 are defined as respectively different values within a cycle range ofrotated bit sizes 2^(n)(0˜2^(n)−1).

The rotated bit difference value (δS) is represented as a graph thatincreases at a steady slope according to the rotation of the steeringshaft. That is, the difference between the first rotated bit value S1and the second rotated bit value S2 is calculated as the rotated bitdifference value (δS). Here, if the rotated bit difference value (δS) isdetected to be below 0, the rotated bit size 2^(n) for one cycle isadded to δS or S1.

By multiplying the gain value to the rotated bit difference value (δS),the steering angle (θ) can be derived. For example, when the rotated bitdifference value (δS) is 200 bits and the gain is 3.6, the steeringangle can be derived as follows: 200×3.6=720°.

FIG. 8 is a flowchart of a steering angle sensing method according to afirst embodiment.

Referring to FIG. 8, the shaft gear rotates through the rotation of thesteering shaft, and the first and second sub gears having respectivelydifferent gear ratios rotate according to the rotation of the shaftgear. Here, the first and second magnets coupled on the axes of thefirst and second sub gears rotate in S101. The gear ratio of the firstsub gear is smaller than that of the second sub gear.

When the magnetic fields of the first and second magnets change, thefirst and second angle detecting portions output in S103 a first andsecond rotated bit value S1 and S2 as rotated angles according to thechanges in magnetic fields of the first and second magnets.

When the first and second rotated bit values S1 and S2 are inputted inthe steering angle calculating portion, the second rotated bit value S2is subtracted from the first rotated bit value S1, and the rotated bitdifference value (δS) is derived in S105. It is determined in S107whether the derived rotated bit difference (δS) is 0 or more. Here, therotated bit difference value (δS) is derived by subtracting the rotatedbit value of the magnet with the higher rotating cycle from the rotatedbit value of the magnet with the lower rotating cycle.

If the rotated bit difference is determined to be 0 or more in S107, thegain (G) value is multiplied to the subtracted result, to obtain thesteering angle (θ=δS×G) in S111. Here, the gain value is a preset value.

If the subtracted result is less than 0, the bit size for one cycle(2^(n)) is added to the first rotated bit value (S1) in S109, and therevised first rotated bit value and the second rotated bit value aresubtracted, and S105 is revisited to obtain the rotated bit difference(δS).

FIG. 9 is a flowchart of a steering angle sensing method according to asecond embodiment.

Referring to FIG. 9, the shaft gear rotates due to the rotation of thesteering shaft, and the first and second sub gears having different gearratios rotate due to the rotation of the shaft gear. Here, the first andsecond magnets that are coupled on the axes of the first and second subgears rotate in S121. The gear ratio of the first sub gear is smallerthan that of the second sub gear.

When the magnetic fields of the first and second magnets are altered,the first and second angle detecting portions output first and secondrotated bit values S1 and S2 corresponding to the rotated angles of thefirst and second magnets in S123.

When the first and second bit values S1 and S2 are inputted by thesteering angle calculating portion, the second rotated bit value S2 issubtracted from the first rotated bit value S1 to obtain the rotated bitdifference δS in S125. It is determined in S127 whether the rotated bitdifference is 0 or higher.

If the rotated bit difference δS is 0 or higher, a gain (G) value ismultiplied to the subtracted result to detect the steering angle(θ=δS×G) in S131. Here, the gain value is a preset value.

If the rotated bit difference δS is less than 0, a one cycle bit size2^(n) is added to the obtained rotated bit difference to revise therotated bit difference in S129, and the steering angle is obtained inS131.

While the present invention has been described and illustrated hereinwith reference to the preferred embodiments thereof, it will be apparentto those skilled in the art that various modifications and variationscan be made therein without departing from the spirit and scope of theinvention. Thus, it is intended that the present invention covers themodifications and variations of this invention that come within thescope of the appended claims and their equivalents.

INDUSTRIAL APPLICABILITY

In the steering angle sensing apparatus and method of embodimentsherein, by outputting changes in magnetic fields (of magnets that rotateat respectively different cycles according to the rotation of a shaftgear coupled to a steering shaft) as digital data, an absolute steeringangle can be obtained using a simple calculation, for a high industrialapplicability.

Also, because there is no need to convert analog signals to digitalsignals, the chance of errors occurring during the conversion process isreduced.

Furthermore, due to there being no signal converting process, thereliability and processing speed are increased, and the price is reduceddue to the omission of an analog/digital converter.

Additionally, a smaller steering angle sensing apparatus can beprovided.

Moreover, a multi-purpose steering sensor combining a steering anglesensing apparatus with a torque sensing apparatus can be provided.

1. A steering angle sensing apparatus comprising: a case; a covercoupled to the case; an output shaft of a steering torque sensor;wherein at least a portion of the output shaft is disposed between thecase and the cover; a shaft gear directly coupled to the output shaft; afirst sub gear rotating with the shaft gear; a second sub gear having agear ratio different from a gear ratio of the first sub gear androtating with the shaft gear; a first magnet coupled to the first subgear; a second magnet coupled to the second sub gear; a first and asecond angle detecting portion disposed on the cover and spaced apredetermined distance respectively from the first and second magnets,and respectively outputting rotated bit values corresponding to rotatedangles of the first and second magnets, wherein the first and secondangle detecting portions are rotary hall integrated circuits; and asteering angle calculating portion configured to calculate an absolutesteering angle from the rotated bit values, wherein the steering anglecalculating portion calculates a difference between the rotated bitvalues outputted by the first and second angle detecting portions, andmultiplies a uniform gain value to the calculated difference between therotated bit values.
 2. The steering angle sensing apparatus according toclaim 1, wherein the output shaft is coupled to a steering shaft.
 3. Thesteering angle sensing apparatus according to claim 1, wherein the shaftgear includes a protrusion and the output shaft includes a slot, whereinthe protrusion is coupled to the slot.
 4. The steering angle sensingapparatus according to claim 1, comprising steering shaft inserted intothe output shaft.
 5. The steering angle sensing apparatus according toclaim 1, wherein the second sub gear is engaged with the first sub gear.6. The steering angle sensing apparatus according to claim 1, whereinthe first sub gear is formed in the same horizontal plane as the secondsub gear.
 7. The steering angle sensing apparatus according to claim 1,wherein the second sub gear is directly engaged to an outercircumference or an inner circumference of the first sub gear.
 8. Thesteering angle sensing apparatus according to claim 1, comprising aconnecting gear formed at a side of the first sub gear and engaged withthe second sub gear.
 9. The steering angle sensing apparatus accordingto claim 1, wherein the first and second magnets comprise a permanentmagnet having at least two poles.
 10. The steering angle sensingapparatus according to claim 1, wherein the steering angle calculatingportion calculates the difference between the rotated bit values throughsubtracting a rotated bit value of a magnet from the first and secondmagnets with a longer rotation cycle from a rotated bit value of amagnet from the first and second magnets with a shorter rotation cycle.11. The steering angle sensing apparatus according to claim 1, whereinwhen the difference between the rotated bit values is 0, the steeringangle calculating portion adds a bit size of one cycle to a rotated bitvalue of a magnet from the first and second magnets with a shorterrotation cycle or the difference between the rotated bit values.
 12. Thesteering angle sensing apparatus according to claim 1, wherein thedifference between the rotated bit values satisfies 0≦ the differencebetween the rotated bit values ≦2^(n)−1, where 2^(n) is a digital bitnumber for one cycle, and n is a number of bits.
 13. A steering anglesensing apparatus comprising: a shaft gear coupled to a steering shaft;a first sub gear rotating with the shaft gear; a second sub gear engagedwith the first sub gear, and having a rotation cycle longer than arotation cycle of the first sub gear; a first magnet rotating with thefirst sub gear; a second magnet rotating with the second sub gear; afirst and a second angle detecting portion spaced a predetermineddistance respectively from the first and second magnets, andrespectively outputting rotated bit values corresponding to rotatedangles of the first and second magnets; and a steering angle calculatingportion that calculates a difference between the rotated bit valuesoutputted by the first and second angle detecting portions throughsubtracting a rotated bit value of the second magnet from a rotated bitvalue of the first magnet, wherein when the difference between therotated bit values is 0 or less, the steering angle calculating portionadds a bit size of one cycle to the rotated bit value of the firstmagnet or the difference between the rotated bit values, and multipliesa uniform gain value to the calculated difference between the rotatedbit values to obtain an absolute steering angle, wherein the differencebetween the rotated bit values is linearly changed in range of an entirelock-to-lock steering angle of the steering shaft, and wherein thedifference between the rotated bit values is uniquely corresponded tothe absolute steering angle.
 14. The steering angle sensing apparatusaccording to claim 13, wherein the second sub gear is engaged to anouter circumference or an inner circumference of the first sub gear. 15.The steering angle sensing apparatus according to claim 13, wherein thefirst and second magnets comprise a permanent magnet having at least twopoles.
 16. The steering angle sensing apparatus according to claim 13,wherein the first and second angle detecting portions are rotary hallintegrated circuits.
 17. The steering angle sensing apparatus accordingto claim 13, wherein the difference between the rotated bit valuessatisfies 0≦ the difference between the rotated bit values ≦2^(n−1),where 2^(n) is a digital bit number for one cycle, and n is a number ofbits.
 18. The steering angle sensing apparatus according to claim 13,comprising a storage for storing a rotated bit value inputted in thesteering angle calculating portion, a rotated bit difference, a gainvalue, and a steering angle.
 19. The steering angle sensing apparatusaccording, to claim 13, wherein the shaft gear is coupled to an outercircumference of an output shaft of a steering torque sensing device.20. A steering angle sensing method comprising: rotating a shaft gearcoupled to a steering shaft; rotating first and second sub gears withmutually different gear ratios together with the shaft gear, wherein thesecond sub gear has a rotation cycle longer than a rotation cycle of thefirst sub gear; outputting first and second rotated bit valuescorresponding to changes in magnetic fields of first and second magnets,the first magnet coupled on an axis of the first sub gear and the secondmagnet coupled on an axis of the second sub gear; obtaining a differencebetween the first and second rotated bit values; and obtaining anabsolute steering angle through multiplying the difference first andsecond rotated bit values with a uniform gain value, wherein thedifference between the first and second rotated bit values is calculatedthrough subtracting the second rotated bit value from the first rotatedbit value, wherein when the difference between the first and secondrotated bit values is less than 0, a bit size of one cycle is added tothe first rotated bit value or the difference between the first andsecond rotated bit values, wherein the difference between the first andsecond rotated bit values is linearly changed in range of an entirelock-to-lock steering angle of the steering shaft, and wherein thedifference between the first and second rotated bit values is uniquelycorresponded to the absolute steering angle.